608 research outputs found
On the leading OPE corrections to the ghost-gluon vertex and the Taylor theorem
This brief note is devoted to a study of genuine non-perturbative corrections
to the Landau gauge ghost-gluon vertex in terms of the non-vanishing
dimension-two gluon condensate. We pay special attention to the kinematical
limit which the bare vertex takes for its tree-level expression at any
perturbative order, according to the well-known Taylor theorem. Based on our
OPE analysis, we also present a simple model for the vertex, in acceptable
agreement with lattice data.Comment: Final version published in JHE
The strong coupling constant at small momentum as an instanton detector
We present a study of at small p computed from the lattice.
It shows a dramatic law which can be understood within an
instanton liquid model. In this framework the prefactor gives a direct measure
of the instanton density in thermalised configurations. A preliminary result
for this density is 5.27(4) fm^{-4}.Comment: 12 pages, 4 figure
Testing Landau gauge OPE on the Lattice with a Condensate
Using the operator product expansion we show that the correction
to the perturbative expressions for the gluon propagator and the strong
coupling constant resulting from lattice simulations in the Landau gauge are
due to a non-vanishing vacuum expectation value of the operator .
This is done using the recently published Wilson coefficients of the identity
operator computed to third order, and the subdominant Wilson coefficient
computed in this paper to the leading logarithm. As a test of the applicability
of OPE we compare the estimated from the gluon propagator and
the one from the coupling constant in the flavourless case. Both agree within
the statistical uncertainty: GeV.
Simultaneously we fit \Lams = 233(28) MeV in perfect agreement with previous
lattice estimates. When the leading coefficients are only expanded to two
loops, the two estimates of the condensate differ drastically. As a consequence
we insist that OPE can be applied in predicting physical quantities only if the
Wilson coefficients are computed to a high enough perturbative order.Comment: 15 pages, LaTex file with 5 figure
The anomalous dimension of the gluon-ghost mass operator in Yang-Mills theory
The local composite gluon-ghost operator is analysed in the framework of the algebraic
renormalization in SU(N) Yang-Mills theories in the Landau, Curci-Ferrari and
maximal abelian gauges. We show, to all orders of perturbation theory, that
this operator is multiplicatively renormalizable. Furthermore, its anomalous
dimension is not an independent parameter of the theory, being given by a
general expression valid in all these gauges. We also verify the relations we
obtain for the operator anomalous dimensions by explicit 3-loop calculations in
the MSbar scheme for the Curci-Ferrari gauge.Comment: 12 pages, LaTeX, final version to appear in Phys. Lett.
Preliminary Calculation of from Green Functions with Dynamical Quarks
We present preliminary results on the computation of the QCD running coupling
constant in the scheme and Landau gauge with two flavours of
dynamical Wilson quarks. Gluon momenta range up to about 7 GeV ( 5.6,
5.8 and 6.0) with a constant dynamical-quark mass. This range already allows to
exhibit some evidence for a sizable correction to the asymptotic
behaviour, as in the quenched approximation, although a fit without power
corrections is still possible with a reasonable . Following the
conclusions of our quenched study, we take into account correction to
the asymptotic behaviour. We find , which leads to
. The latter result has to be taken as a
preliminary indication rather than a real prediction in view of the systematic
errors still to be controlled. Still, being two sigmas below the experimental
result makes it very encouraging.Comment: 14 pages, 3 figs., 2 tabs., revte
Remarks on the determination of the Landau gauge OPE for the Asymmetric three gluon vertex
We compute a compact OPE formula describing power corrections to the
perturbative expression for the asymmetric -renormalized
running coupling constant up to the leading logarithm. By the use of the
phenomelogical hypothesis leading to the factorization of the condensates
through a perturbative vacuum insertion, the only relevant condensate in the
game is . The validity of the OPE formula is tested by searching for a
good-quality coherent description of previous lattice evaluations of
-renormalized gluon propagator and running coupling.Comment: 12 pages, 3 figures (2 generated by the macro: axodraw.sty
Instantons and Condensate
We argue that the is similar to .Comment: 6 pages, 1 fig., 1 tab., RevTeX to be use
Wilson Expansion of QCD Propagators at Three Loops: Operators of Dimension Two and Three
In this paper we construct the Wilson short distance operator product
expansion for the gluon, quark and ghost propagators in QCD, including
operators of dimension two and three, namely, A^2, m^2, m A^2, \ovl{\psi} \psi
and m^3. We compute analytically the coefficient functions of these operators
at three loops for all three propagators in the general covariant gauge. Our
results, taken in the Landau gauge, should help to improve the accuracy of
extracting the vacuum expectation values of these operators from lattice
simulation of the QCD propagators.Comment: 20 pages, no figure
Masses and Decay Constants of Heavy-Light Mesons Using the Multistate Smearing Technique
We present results for f_B and masses of low-lying heavy-light mesons.
Calculations were performed in the quenched approximation using multistate
smearing functions generated from a spinless relativistic quark model
Hamiltonian. Beta values range from 5.7 to 6.3, and light quark masses
corresponding to pion masses as low as 300 MeV are computed at each value. We
use the 1P--1S charmonium splitting to set the overall scale.Comment: 9 pages, 13 figures, and 5 tables as a single 193K compressed and
uuencoded Postscript file, FERMILAB--CONF--93/376-
Gauge invariance of dimension two condensate in Yang-Mills theory
Gauge independence of dimension two condensate in Yang-Mills theory is
demonstrated by using a noncommutative theory technique.Comment: 7 page
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